Calculate and show Ambient shadow.

Basically we compute the shadow as a strip of triangles, whose alpha value
is the strength of the shadow.
We use the normal to extend the geometry.
And we use static function and try to avoid new/malloc in the computation.

Change-Id: I382286f1cad351bd5ff983f76f446c075819dcaf
diff --git a/libs/hwui/Caches.cpp b/libs/hwui/Caches.cpp
index f8d3589..5b751b9 100644
--- a/libs/hwui/Caches.cpp
+++ b/libs/hwui/Caches.cpp
@@ -473,7 +473,7 @@
 // Meshes and textures
 ///////////////////////////////////////////////////////////////////////////////
 
-void Caches::bindPositionVertexPointer(bool force, GLvoid* vertices, GLsizei stride) {
+void Caches::bindPositionVertexPointer(bool force, const GLvoid* vertices, GLsizei stride) {
     if (force || vertices != mCurrentPositionPointer || stride != mCurrentPositionStride) {
         GLuint slot = currentProgram->position;
         glVertexAttribPointer(slot, 2, GL_FLOAT, GL_FALSE, stride, vertices);
@@ -482,7 +482,7 @@
     }
 }
 
-void Caches::bindTexCoordsVertexPointer(bool force, GLvoid* vertices, GLsizei stride) {
+void Caches::bindTexCoordsVertexPointer(bool force, const GLvoid* vertices, GLsizei stride) {
     if (force || vertices != mCurrentTexCoordsPointer || stride != mCurrentTexCoordsStride) {
         GLuint slot = currentProgram->texCoords;
         glVertexAttribPointer(slot, 2, GL_FLOAT, GL_FALSE, stride, vertices);